Contact structure of a semiconductor device

ABSTRACT

A method for fabricating a contact of a semiconductor device includes the steps of forming a dielectric layer having a contact hole on a semiconductor substrate, forming an out-gassing barrier layer comprising a poly-silicon layer to cover at least inner walls of the contact hole in order to prevent undesired out-gassing from the dielectric layer, and depositing an aluminum layer on the out-gassing barrier layer. The contact structure of the semiconductor device includes the aluminum layer filled in the contact layer formed on the semiconductor substrate, and the out-gassing barrier layer formed under the aluminum layer to prevent out-gassing from the dielectric layer. A fine contact can be formed along with the aluminum layer, thereby realizing the contact structure of a lower contact resistance. As a result, it is possible to realize stabilization of an overall contact resistance of the semiconductor device.

This is a division of U.S. application Ser. No. 11/423,054 filed Jun. 8,2006, which claims the priority benefit under USC 119 of KR 2005-0134304filed Dec. 29, 2005, the entire respective disclosures of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and, moreparticularly, to a contact structure of a semiconductor device using analuminum layer, and a method for fabricating the same.

2. Description of the Related Art

Reduction in design rule of a semiconductor device has resulted ingradual deterioration of a contact hole filling properties. Accordingly,to effectively fill a contact hole of a high aspect ratio with a finecritical dimension, a method for forming a tungsten contact has beenintroduced, which employs a chemical vapor deposition (CVD) process todeposit tungsten.

Meanwhile, as an operating speed of a higher level, for example, anoperating speed of 667 MHz or more has been required for semiconductordevices, for example, graphic memory devices, reduction of contactresistance has been also required. Because tungsten has a relativelyhigh specific resistance of about 20 μΩcm or more, it has a limit tosatisfy the requirement for a lower contact resistance. For example, acontact area of 0.025 μm² exhibits a considerably high contactresistance of several ohms (Ω).

As a conductive material with a lower specific resistance than that oftungsten, aluminum can be considered. However, when filling a contacthole with an aluminum layer, gases generated from an inter-dielectriclayer constituting a side wall of the contact obstruct deposition of thealuminum layer, thereby deteriorating step coverage of the aluminumlayer.

FIG. 1 is a cross-sectional view schematically illustrating aconventional method for forming a contact of a semiconductor device.

Referring to FIG. 1, for the conventional contact forming method, anupper dielectric layer 23 is formed to cover a lower wire 30 formed on alower dielectric layer 21 of a semiconductor substrate 10. Then, acontact hole 25 is formed to penetrate the upper dielectric layer 23,and is filled with an aluminum layer by deposition. Here, the depositionof aluminum (Al) is obstructed by gases discharged from a dielectricmaterial such as BPSG constituting the upper dielectric layer 23, sothat the step coverage of the Al layer is deteriorated.

The materials discharged from the upper dielectric layer 23 may includemoisture contained therein upon application of BPSG, or compounds whichcontain boron (B), phosphorus (P) and the like. Such dischargedmaterials are discharged to an outside of the upper dielectric layer 23at temperatures for deposition.

For BPSG, it is measured that a material having an atomic weight of 18,for example, moisture, is primarily discharged in a large amount within1 to 4 seconds at a temperature of about 200° C. In addition, it ismeasured that the material having an atomic weight of 18 is alsosecondarily discharged in a large amount within 1 to 2 seconds below atemperature of about 300° C., and that the material is tertiarilydischarged in a large amount within 1 second at a temperature of about400° C. although the discharge amount of the material is relativelyreduced.

The discharged gases can serve as elements of obstructing deposition ofthe Al layer, and lead to deterioration in filling property of the Allayer in the contact hole 25. Thus, it is urgently needed to develop amethod, which can solve the obstruction of the discharged gases againstdeposition of the Al layer when forming the contact using the Al layer.

SUMMARY OF THE INVENTION

Disclosed herein is a contact of a semiconductor device, and a methodfor fabricating the same.

According to one aspect of the present invention, a method forfabricating a contact of a semiconductor device includes forming adielectric layer having a contact hole on a semiconductor substrate;forming an out-gassing barrier layer containing silicon (Si) to preventdischarge of gas from the dielectric layer; forming a metal wettinglayer on the barrier layer; and depositing an aluminum layer on thewetting layer.

The method may further include annealing to induce silicidation reactionbetween the poly-silicon layer and the metal wetting layer.

Annealing may be performed at a temperature of at least 400° C.

The poly-silicon layer may be deposited in a tube furnace to cover atleast walls of the contact hole.

The method also may include pre-cleaning the poly-silicon layer using afluorine containing gas before forming the aluminum layer.

The wetting layer may include either a titanium layer or atitanium/titanium nitride/titanium layer.

The second aluminum layer may be deposited by physical vapor deposition(PVD) using an aluminum target containing 2% or less of Si to preventreaction with silicon of the out-gassing barrier layer.

According to another aspect of the present invention, a method forfabricating a contact of a semiconductor device includes forming adielectric layer having a contact hole on a semiconductor substrate;forming an out-gassing barrier layer comprising a poly-silicon layer tocover at least inner walls of the contact hole in order to preventundesired gas from being discharge from the dielectric layer; anddepositing an aluminum layer on the out-gassing barrier layer.

The method may further include doping P or Ge to the poly-silicon layerto impart conductivity to the poly-silicon layer.

The aluminum layer forming step may include forming a metal wettinglayer on the out-gassing barrier layer; forming a first aluminum layeron the wetting layer by CVD; forming a second aluminum layer on thefirst aluminum layer by PVD; and annealing the first and second aluminumlayers at a temperature of at least 400° C.

According to yet another aspect of the present invention, a contactstructure of a semiconductor device may include an aluminum layer to befilled in a contact hole formed in a dielectric layer on a semiconductorsubstrate, and an out-gassing barrier layer formed under the aluminumlayer to prevent out-gassing from the dielectric layer, the out-gassingbarrier layer containing Si.

The out-gassing barrier layer may include a conductive poly-siliconlayer. The contact structure may further comprise a metal wetting layerat an interface between the conductive poly-silicon layer and thealuminum layer.

The out-gassing barrier layer may comprise a metal silicide layer.

According to the present invention, the method for fabricating thealuminum contact structure and the contact structure formed thereby canprevent deposition property from being deteriorated due to theout-gassing when forming the contact by means of the out-gassing barrierlayer which provides an excellent coverage property for the walls of thecontact hole.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the disclosure, reference should bemade to the following detailed description and accompanying drawingwherein:

FIG. 1 is a cross-sectional view schematically illustrating aconventional method for forming a contact of a semiconductor device; and

FIGS. 2 to 6 are cross-sectional views schematically illustrating acontact structure of a semiconductor device in accordance with apreferred embodiment of the present invention, and steps of a method forforming the contact structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described indetail with reference to the accompanying drawings. It should be notedthat the present invention may be embodied in various forms, and is notlimited to the embodiments described herein. The embodiments of thepresent invention are provided for clear description of the invention tothose skilled in the art.

According to one preferred embodiment of the present invention, a layerhaving an excellent coverage property, for example, a conductivepoly-silicon layer is introduced as an out-gassing barrier layer towalls of a contact hole in order to prevent deposition property of analuminum layer from being deteriorated due to out-gassing from adielectric layer upon deposition of the aluminum layer for filling thecontact hole.

Preferably, the out-gassing barrier layer is formed to cover at leastthe walls of the contact hole such that a portion of the dielectriclayer constituting the walls of the contact hole is not exposed to anoutside. Meanwhile, because an aspect ratio of the contact hole issignificantly increased due to reduction in design rule of thesemiconductor device, it is relatively difficult to form such anout-gassing barrier layer via general CVD or PVD.

A poly-silicon layer is formed in a tube furnace to realize excellentstep coverage property. In this case, it is possible to form apoly-silicon layer having step coverage of 95% or more in view ofdeposition characteristic of the tube furnace.

On the out-gassing barrier layer of the poly-silicon layer, a titaniumlayer, a combination layer of titanium/titanium nitride, a combinationlayer of titanium/titanium nitride/titanium may be deposited as awetting layer prepared for deposition of the aluminum layer. The wettinglayer serves to induce deposition of the aluminum layer while reducingcontact resistance between the aluminum layer and the poly-siliconlayer.

Such a wetting layer is sufficiently deposited to cover at least abottom surface of the contact hole such that the aluminum layer issufficiently filled in the contact hole without generating defects, forexample, voids. Accordingly, coverage of the wetting layer on the wallsof the contact hole can be slightly deteriorated. However, because theout-gassing barrier layer is introduced at a lower portion of thewetting layer to cover the walls of the contact hole and prevents theout-gassing therefrom, it is possible to effectively prevent dischargedgas from obstructing deposition of the Al layer.

FIGS. 2 to 6 are cross-sectional views schematically illustrating acontact structure of a semiconductor device in accordance with apreferred embodiment of the present invention, and steps of a method forforming the contact structure.

Referring to FIG. 2, after forming a lower wire 300 on a lowerdielectric layer 210 of a semiconductor substrate 100, an upperdielectric layer 230 is formed to cover the lower wire 300. A contacthole 205 is formed to penetrate the upper dielectric layer 230 and alignwith the lower wire 300.

Then, a primary pre-cleaning process is performed to clean an uppersurface of the lower wire 300 exposed at the bottom of the contact hole205. Here, the primary pre-cleaning process may be performed in a way ofdry cleaning using a fluorine containing gas as a source.

Referring to FIG. 3, an out-gassing barrier layer 400 is formed alongthe upper dielectric layer 230 within the contact hole 205. Theout-gassing barrier layer 400 is introduced to prevent depositionproperty from being lowered due to out-gassing from the upper dielectriclayer 230 when depositing an aluminum layer and the like which will befilled in the contact hole 205. Accordingly, the out-gassing barrierlayer 400 is preferably formed as a layer, which has an excellent stepcoverage property with respect to a subsequent wetting layer, in orderto ensure that the out-gassing barrier layer 400 covers at least wallsof the contact hole 205.

As for the out-gassing barrier layer 400, it is preferable to use asilicon containing layer, such as a conductive poly-silicon layer, whichcan be deposited in a tube furnace. By depositing the poly-silicon layerwithin the tube furnace, it is possible to realize the step coverage ofthe poly-silicon layer to a high level of 95% or more. Accordingly, thewalls of the contact hole 205 are sufficiently shielded with thepoly-silicon layer.

As for the wetting layer, a metal layer such as a titanium (Ti) layermay be used, and deposited by CVD or PVD. For the case where the metallayer is used as the wetting layer, as the contact hole 205 is decreasedin area, but increased in aspect ratio, it is difficult to realize thestep coverage of 95% or more which is required for the out-gassingbarrier layer 400 as in the poly-silicon layer. For example, because acontact area of 0.025 μm² results in a very high aspect ratio of thecontact hole 205, it is necessary for the out-gassing barrier layer 400to provide a higher step coverage. In addition, since the poly-siliconlayer deposited in the tube furnace may be denser than the Ti-layeraccording to the deposition property, the poly-silicon layer cansecurely prevent the out-gassing.

To prevent an overall resistance of an embedded contact structure frombeing reduced due to the poly-silicon layer, impurities may be doped tothe poly-silicon layer to impart higher conductivity thereto afterdepositing the poly-silicon layer. For example, phosphorus (P) orgermanium (Ge) may be doped to increase the conductivity of thepoly-silicon layer.

Referring to FIG. 4, a secondary pre-cleaning process to clean thesurface of the out-gassing barrier layer 400 of the poly-silicon layeris performed, thereby removing contaminants from the surface of thepoly-silicon layer. At this time, it is preferable that the secondarypre-cleaning process is performed in situ during deposition of asubsequent wetting layer using a fluorine containing gas. Accordingly,it is possible to realize additional reduction in contact resistance.

Referring to FIG. 5, a metal wetting layer 500 is formed on theout-gassing barrier layer 400. The metal wetting layer 500 is formedbefore deposition of a subsequent aluminum contact filling layer, andinduces aluminum deposition. The wetting layer 500 may be formed of atitanium layer or a combination layer of titanium/titaniumnitride/titanium.

In addition, the wetting layer 500 may be deposited by a process, whichcan provide an excellent coverage on the bottom of the contact hole 205,in order to induce the aluminum layer to be sufficiently filled in thecontact hole 205 without defects such as voids. For example, the wettinglayer 500 may be deposited by an ion or ionized metal plasma (IMP)process. Alternatively, the wetting layer 500 may be deposited by aself-ionized plasma type sputtering process when depositing titanium ortitanium nitride.

At this time, to increase a deposition thickness of the wetting layer500 on the bottom of the contact hole 205, a bias applied to a rear sideof the substrate 100 may be maintained at a high level of 200 W or more.Because the out-gassing barrier layer 400 is formed, it is possible toperform the deposition in consideration of a relative coverage propertyof the wetting layer 500 on the bottom of the contact hole 205 ratherthan extension of the wetting layer 500 on the walls of the contact hole205.

Referring to FIG. 6, an aluminum layer 600 may be deposited as a contactfilling layer on the wetting layer 500. At this time, a first aluminumlayer 610 is deposited by the CVD to improve the contact fillingproperty of the aluminum layer 600, and a second aluminum layer 630 isthen deposited by the PVD to reduce contact resistance. At this time, anAl—Si target that contains Si of at most 2% may be used upon depositionof the PVD-Al layer in order to suppress reaction between thepoly-silicon layer and the aluminum layer 600, for example, migration ofaluminum elements to the poly-silicon layer.

Meanwhile, after depositing the aluminum layer 600, that is, afterdeposition of the PVD-Al layer on the CVD-Al layer, annealing may beperformed at a temperature of about 400° C. or more to reduce contactresistance. It can be understood that annealing is performed to realizeimprovement in resistance of the aluminum layer 600. Additionally,annealing can be understood as a process for silicidation of metal, forexample, titanium, constituting the wetting layer 500 and of siliconconstituting the out-gassing barrier layer 400 (see FIG. 4).Accordingly, a metal silicide layer 401 such as a titanium silicidelayer may be formed on the aluminum layer 600. The metal silicide layer401 enables the resistance of the whole contact to be reduced.

Next, an anti-reflection layer (ARC) 700 may be deposited on thealuminum layer 600 in order to suppress scattered reflection by thealuminum layer 600 during exposure of a photolithography process.

The ARC layer 700 may be a titanium nitride layer, a combination layerof titanium/titanium nitride, a combination layer of titaniumnitride/SiON, a combination layer of titanium/titanium nitride/SiON orthe like. The ARC layer 700 may have a thickness of at least 300 Å ormore.

Next, an Al-contact is formed through photolithography and etchingprocesses. As a result, a connection contact to connect the upper andlower wires may be formed to have a lower contact resistance. Thus, itis possible to form a contact with a fine contact area of 0.025 μm² orless and having a lower contact resistance than that of a tungstencontact.

As apparent from the above description, according to the presentinvention, a fine contact, for example, a connection contact having acontact area of about 0.025 μm² can be formed along with an aluminumlayer, thereby realizing a contact structure having lower contactresistance than that of the tungsten contact. As a result, it ispossible to realize stabilization in overall contact resistance of asemiconductor device.

It should be understood that the embodiments and the accompanyingdrawings have been described for illustrative purposes and the presentinvention is limited only by the following claims. Further, thoseskilled in the art will appreciate that various modifications, additionsand substitutions are allowed without departing from the scope andspirit of the invention as set forth in the accompanying claims.

1. A contact structure of a semiconductor device, the structurecomprising: an aluminum layer filled in a contact hole formed in adielectric layer on a semiconductor substrate; an out-gassing barrierlayer formed under the aluminum layer to prevent out-gassing from thedielectric layer, the out-gassing barrier layer comprising a conductivepoly-silicon layer; and, a metal wetting layer at an interface betweenthe conductive poly-silicon layer and the aluminum layer.
 2. A contactstructure of a semiconductor device, the structure comprising: analuminum layer filled in a contact hole formed in a dielectric layer ona semiconductor substrate; and an out-gassing barrier layer formed underthe aluminum layer to prevent out-gassing from the dielectric layer, theout-gassing barrier layer comprising a metal silicide layer.